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    <script>

        var arr = [
            [1,2,3] ,    // arr[0]
            [4,5,6] ,    // arr[1]
            7            // arr[2]
        ] ;

        console.log(arr[0]);

        console.log(arr[0][1]);


        // 二维数组的遍历

        for(var i = 0 ; i < arr.length ; i++) {
            // 判断一下是不是数组
            if(Array.isArray(arr[i])) {
                for(var j = 0 ; j < arr[i].length ; j++) {
                    console.log(arr[i][j]);
                }
            } else {
                console.log(arr[i]);
            }
            
        }



    </script>
    
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